How do pregnancy test kits use monoclonal antibodies to detect HCG?

Sourav PanNovember 9, 2024

Answered step-by-step

Pregnancy test kits utilize monoclonal antibodies to detect the hormone human chorionic gonadotropin (hCG) in a woman’s urine. Here’s how this process works:

Mechanism of Action

1. Detection of hCG:
   • hCG is a hormone produced by the placenta shortly after fertilization and is present in the urine of pregnant women. Pregnancy tests are designed to detect this hormone, which typically appears around 7-10 days after conception and increases rapidly during early pregnancy.
2. Use of Monoclonal Antibodies:
   • The test employs monoclonal antibodies that specifically bind to hCG. These antibodies are highly selective and can differentiate hCG from other similar hormones, such as luteinizing hormone (LH), which is important for ensuring the accuracy of the test.
3. Lateral Flow Assay:
   • Most home pregnancy tests operate using a lateral flow assay system:
   • Sample Application: The user applies a urine sample to the absorbent pad of the test strip.
   • Migration: The urine flows along the strip through capillary action, interacting with the coated antibodies.
   • Formation of Antibody Complexes: If hCG is present in the urine, it binds to the mobile monoclonal antibodies that are conjugated with a detectable marker (often a colored dye or enzyme). This forms an antibody-hCG complex.
4. Visual Indicator:
   • As the complex continues to migrate along the strip, it encounters another set of fixed antibodies located at a designated test line (T-line). If hCG is present, the complex binds to these fixed antibodies, resulting in a color change at the T-line, indicating a positive result.
   • A control line (C-line) is also present on the test strip, which confirms that the test has functioned correctly. This line appears regardless of whether hCG is present and indicates that sufficient sample has been absorbed and that the test is working properly.
5. Interpretation of Results:
   • If both lines (T-line and C-line) appear, it indicates a positive result for pregnancy. If only the C-line appears, it indicates a negative result.

Significance

• High Sensitivity and Specificity: The use of monoclonal antibodies allows for high sensitivity in detecting low levels of hCG, making these tests reliable even in early pregnancy.
• Ease of Use: Pregnancy tests are user-friendly and provide quick results, making them accessible for home use.
• Early Detection: The ability to detect pregnancy shortly after conception allows for timely medical care and decision-making.